More on the PET I/O area size: The 8032 schematics have the ROM for $E*** labeled as a 2316, meaning it being 2k. But they have BA11 still connected, and it is connected to the /CS line as in the 2001N, so it is only selected when /SELE is active ($E***) and A11 is low -> 2k ROM ($E000-$E7FF), no mirror. However, the 8032 PET mask /SELE for the ROM with x8xx, which is active at addresses $*8**. This means the /SELE is _not_ active in $E8**. So despite the labeling it should be possible to use a 4k ROM 2332, which then has A11 at the rigth place and is selected at $E*** except $E8**, et voila, 256 byte I/O space. So for 2k ROMs it should look like open-address space in $E900-$EFFF and for 4k ROMs there is ROM in $E900-$EFFF - no further hardware changes needed! This should also be an easy way to put in almost 2k of own code into the ROM, without using $9*** and $A***. Only you should not use a 4k ROM with the SuperPET, as it uses the $EFE0-$EFFF as I/O space and you then cannot read from there anymore (bus conflict). Of course all this comes without warranty. so long Andre Andre Fachat wrote: > > One more comment to the 2001N schematics. One might wonder why the > ROM for $E*** is selected with /SELE only while the I/O is selected > with /SELE and x8xx. This would suggest that in $E8** both would be > selected and drive the bus, which would fail. > But: The 2316 has a low-active select line at pin 18, where the > 2332 has A11. But only a A11 is written in the schematics, so > you have to guess that the IC (if and only if 2k) is selected only > when A11 is low, i.e. $E000-$E7FF. > And you should better not put a 4k ROM in there :-) > -- Email address may be invalid. Use "fachat AT physik DOT tu-chemnitz DOT de" ------Fight SPAM - join CAUCE http://www.cauce.org------Thanks, spammers... Andre Fachat, Institute of physics, Technische Universitšt Chemnitz, FRG http://www.tu-chemnitz.de/~fachat
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